Washingtonia robusta

Common name

Mexican fan palm, washingtonia palm, skyduster

Description

Stems: Solitary, tapered stem, upright to 22 m tall and 80 cm diameter, covered with a skirt of marcescentmarcescent:
remaining attached after becoming old and withered (e.g., aging leaves of <em>Washingtonia </em>palms suggest the common name, “petticoat palm”)
leaves (unless removed for landscape appeal). Old leafleaf:
in palms -- the leaf blade (which is usually divided into leaflets or leaf segments), the petiole (or leaf stalk) and the sheath (which forms the attachment of the leaf to the stem)
bases usually fall away after many years, to leave a smooth gray stem with closely spaced leafleaf:
in palms -- the leaf blade (which is usually divided into leaflets or leaf segments), the petiole (or leaf stalk) and the sheath (which forms the attachment of the leaf to the stem)
scar rings. Leaves: Costapalmate, induplicateinduplicate:
Most palm leaflets or leaf segments are obviously folded. If the folds create a V-shape, with the midrib lower than the margins (so that rain might fall "into a valley"), the folding is induplicate.
, split about half the blade length into numerous segments with stiff tips and threads (marginal fibers) hanging between segments. Many bright green leaves form a full crown. Petioles split, armed with curved teeth along orange-colored margins. The adaxialadaxial:
toward the axis or the side of an organ facing toward the axis (<strong>ad </strong>as in <strong>ad</strong>here); for example, the upper surface of a leaf blade or petiole
hastula is prominent with tattered, papery margins. The base of the lower surface of the leafleaf:
in palms -- the leaf blade (which is usually divided into leaflets or leaf segments), the petiole (or leaf stalk) and the sheath (which forms the attachment of the leaf to the stem)
blade densely covered with near white pubescence. Reproductive characters: Inflorescences are numerous, branched to at least three orders, and project from the crown extending beyond the leaves. Individual flowers are bisexual, white. Fruits are spherical to pear-shaped, up to 1 cm in diameter, and brownish-black to black when ripe.

Diagnostic features

Tapered stem, roughly twice as wide at the base as the crown, and bright green leaves forming a dense crown

May be confused with

Washingtonia filifera, but that species has a massive, columnar stem and grayish-green leaves forming an open crown while W. robusta has tapered stems, bright or somewhat olive green leaves with shorter petioles forming a dense crown

Distribution

Native to northwestern Mexico

Additional comments

The two Washingtonia species hybridize freely, making identification of cultivated palms difficult. In Florida, W. robusta is more often planted; in California and Arizona, both are planted, but W. filifera is more common. Both species are planted in drier areas of Hawaii, but W. robusta is much more common.

This species has been included by The University of Georgia Center for Invasive Species and Ecosystem Health as an invasive species in California, Florida and Hawaii. Click here for more details.

The Florida Exotic Pest Plant Council lists this species as a Category II invasive: exotic plants that show signs of increasing in abundance, but that have not yet altered native plant communities. Click here for more details.

Scientific name

Washingtonia robusta H.Wendl.

Family

Arecaceae/Palmae

Synonyms

Neowashingtonia robusta (H.Wendl.) A. Heller

Washingtonia filifera var. robusta (H.Wendl.) Parish

Washingtonia gracilis Parish